1. Field of the Invention
The present invention relates to a speech processing device, a speech processing method, and a speech processing program.
2. Description of Related Art
A sound emitted in a room is repeatedly reflected by walls or installed objects to cause reverberations. In speeches recorded in a room, reverberations based on previously-uttered speech are added to currently-uttered speech. When the recorded speeches are subjected to a speech recognizing process, the speech recognition rate thereof may be lower than that of the original speech. Therefore, reverberation reducing techniques of removing reverberation components from speeches recorded in reverberation environments have been developed.
For example, Japanese Unexamined Patent Application, First Publication No. 2011-065128 (Patent Document 1) describes a reverberation removing device including weighting coefficient creating means for estimating the ratio of energy of a sound output from a sound source prior to an observation point of time with respect to the observed energy of a sound based on a given reverberation time, power spectrum storage means for storing the energy of a sound output prior to the observation point of time, and reverberation component subtracting means for subtracting the energy, which is output prior to the observation point of time and stored in the power spectrum storage means, from the energy of the observed sound, by using a weighting coefficient. In the technique described in Patent Document 1, only reverberation components are subtracted from the observed energy of a sound.
In general, an uttered speech has different sound energy depending on words; however, the technique described in Patent Document 1 estimates sound energy based on the reverberation time and does not consider differences between words. Accordingly, since all the energy based on reverberations cannot be removed from the currently-observed sound energy, it may not be possible to satisfactorily improve speech recognition accuracy.